The piloting of any aircraft necessitates knowing its relative speed with respect to the air, that is to say to the relative wind. This speed is determined with the help of probes measuring the static pressure Ps and the total pressure Pt, as well sensors measuring the angle of incidence α and the sideslip angle β. α and β provide the direction of the speed vector in a reference system related to the aircraft and Pt-Ps provides information which, in combination with the air temperature, makes it possible to calculate the modulus of that speed vector. These five aerodynamic parameters therefore make it possible to determine the speed vector of any aircraft, such as for example an aeroplane or a helicopter.
The total pressure Pt is usually measured using a so-called Pitot tube. This is a tube that is open at one of its ends and obstructed at the other. The open end of the tune substantially faces the airflow.
The airstream situated upstream of the tube is progressively slowed down until it reached a virtually zero speed at the intake of the tube. The slowing down of the speed of the air increases the pressure of the air. This increased pressure forms the total pressure Pt of the airflow. The air pressure existing inside the Pitot tube is measured.
In order to be able to operate in humid conditions, this Pitot tube is electrically heated. The heating prevents the tube from being obstructed by water or even by ice during flights in icing conditions and makes it possible to remove all traces of humidity during operation on the ground. This tube is provided with one or more bleed holes and water traps in order to prevent any rising of water in the total pressure ducting. The bleed holes make it possible to evacuate the water that has penetrated into the Pitot tube. The nominal operation of the Pitot tube involves heating in order to prevent the accumulation of water. In order to carry out a correct total pressure measurement, the Pitot tube is mounted on a mast making it possible to distance the tube from the skin of the aircraft and thus to carry out the pressure measurement out of the boundary layer of the flow developing in the vicinity of the skin. The mast can be fixed or mobile in the case of a probe designed to be oriented along the axis of the airflow.
The heating of the probe is commonly carried out by means of a heating resistor produced in the form of a wire wound in the body of the probe, that is to say both in the mast and in the Pitot tube. The heating of the probe can be regulated by measuring the temperature of the probe in order to adapt the electrical consumption to the external conditions resulting in the cooling of the probe. This type of regulation however necessitates a large maximum electrical power in order to achieve adequate heating of the probe.
At present, it is being sought to reduce all forms of energy consumption and the invention is included in this objective by making it possible to reduce the maximum power necessary for the heating in order to allow a correct measurement of the total pressure in all of the conditions encountered by the aircraft.